1. Field
Aspects of embodiments of the present invention relate to catheters and, in particular, to a catheter with improved temperature measurement capability.
2. Description of Related Art
Catheters have been in common use in medical practice for many years. Applications of catheters include stimulating and mapping electrical activity in the heart and ablating sites of aberrant electrical activity. Such catheters are also referred to as electrode catheters. In use, an electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the location of interest within the body, e.g., the chamber of the heart where aberrant electrical activity within the heart is located.
Once the catheter reaches the intended location inside the patient's body, the physician uses an ablation procedure to destroy the tissue causing the aberrant electrical activity in an attempt to remove the electrical signal irregularities and restore normal heart beat or at least an improved heart beat. A typical ablation procedure involves providing a reference electrode, generally taped to the skin of the patient. RF (radio frequency) current is applied to the tip electrode, and current flows through the media that surrounds it, i.e., blood and tissue, toward the reference electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive. During this process, heating of the electrode also occurs as a result of conduction from the heated tissue to the electrode itself. If the electrode temperature becomes sufficiently high, a thin transparent coating of dehydrated blood protein can form on the surface of the electrode. If the temperature continues to rise, this dehydrated layer can become progressively thicker, resulting in char and/or thrombus on the electrode surface. The creation of char and thrombus is unsafe, as the char and thrombus can be dislodged from the electrode during the procedure or during removal of the catheter after the procedure.
In clinical practice, it is desirable to reduce or eliminate the formation of char and thrombus and, for certain cardiac arrhythmias, to create larger and/or deeper lesions. One method for accomplishing this end is to monitor the temperature of the ablation electrode and to control the RF current delivered to the ablation electrode based on this temperature. If the temperature rises above a pre-selected value, the current is reduced until the temperature drops below this value. Therefore, the tip of the catheter, e.g., a tip ablation electrode, is equipped for temperature measurement. Among the many temperature transducers available for temperature measurement, thermocouple (TC) is commonly used for its simple construction and ruggedness.
Using TC as temperature sensor requires the use of special cables and connectors made of the same materials as the TC wires, otherwise, material transition in the signal path (e.g., connectors) forms additional junctions of dissimilar metal and additional thermal junctions. However, there are no known off-the-shelf connectors for disposable medical device (e.g., catheter) that are implemented with TC materials such as constantan pins and sockets, and such pins and sockets make a challenging design in conjunction with other medical device connector requirements such as high mating cycles requirement, and high pin density and quality of connection. Therefore, the common disposable medical device is typically connected through off-the-shelf connectors that do not use the appropriate TC material. As such, any material differences between the two sides of the connector translate to measurement error.
Accordingly, it is desirable to provide an improved catheter equipped with TC for temperature measurement. In particular, it is desirable to reduce the measurement errors of TC caused by additional junctions of dissimilar metals and additional thermal junctions.